Investigation into Anaerobic Respiration of Yeast

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October 2004                Pia Potter-Farrant 11BT

GCSE Biology Coursework:

Investigation into Anaerobic Respiration of Yeast

In this piece of coursework I will experimenting with yeast. I will be aiming to find out how temperature affects the rate of respiration of yeast. I will research thoroughly the effects of temperature on respiration of yeast by using a variety of resources such as books amd the internet. This will help me gain a solid knowledge of yeast and respiration and will aid me in making an accurate hypothesis which will hopefully be reflected in my experiments.


I am aiming to carry out a range of experiments to find out how the rate of respiration of yeast is affected by temperature. I will also try and find the optimum temperature for which respiration works best in yeast. I will aim to carry out my experiments safely and I will aim to achieve accurate results which will hopefully support my background research and hypothesis.

Background Information

From my research I have found that:

Yeast is a tiny micro-organism with plant like structures or it can also exist as a form of fungi. It is so minute it can only be viewed under a microscope. Yeast can survive in a number of different environments, as it exists as several different species it can adapt accordingly. It exists in or on all living matter such as soil, water, air etc… As a living organism yeast requires water and sugar, as well as an adequate climate to survive, with albumen or nitrogenous material as necessary additions in order for yeast to thrive. Yeast also grows rapidly, reproducing asexually.

        Respiration is a process that takes place in all living cells. Yeast can respire aerobically or anaerobically, however for alcohol to be produced yeast must respire anaerobically. Respiration converts sugars taken in by the organism into energy. It is the controlled breakdown of carbohydrates to make energy. The usable form of energy for most living organisms is adenosine triphosphate (ATP), the other products of respiration being carbon dioxide and water. The reaction taking place in aerobic respiration is:

C6H12 O6+ 6O2 -> 6CO2+ 6H2O + ATP


This reaction requires oxygen and is the most viable method of respiration. Cellular respiration has three main stages; Glycolysis, the Krebs cycle and electron transport. Glycolysis splits up the sugars involved in respiration. It can take place with or without oxygen and is the first stage of aerobic respiration. It breaks down the carbohydrate into 2 ATP molecules and 2 high energy electron carrying molecules. The next stage is the Krebs cycle. High energy storing compounds nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD) are reduced and carry electrons to the next stage. Electron transport requires oxygen to take place. It takes place in the mitochondria and the electrons are passed to oxygen and consequently, ATP is produced.

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        However, respiration of yeast can also take place anaerobically. This process does not require oxygen and is referred to as fermentation. This process partially breaks down carbohydrates and it obtains a small amount of energy, again in the form of ATP. Pyruvic acid has to be broken down in respiration when formed by breaking down of glucose molecules, this can't be done in the same way as in aerobic respiration. When anaerobic respiration is taking place carbon dioxide and ethanol is formed. The reaction for this process is:        

C6H12 O6 -> 2C2H5 OH + 2CO2 + ATP

Enzymes are biological catalysts; they ...

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